Forest establishment and water quality characteristics as influenced by spoil type on a loose-graded surface mine in eastern Kentucky

Six research plots were established on a surface mine for the purpose of evaluating the forest productivity potential and hydrological and water quality characteristics of three different loose-graded spoil types. The three spoil types were: (1) predominately brown, weathered sandstone (BROWN); (2) predominately gray, un-weathered sandstone (GRAY); and (3) mixed weathered and un-weathered sandstones and shale material (MIXED). The average area of the six plots was approximately 3,658 m². The physical and chemical soil characteristics that gave the BROWN spoil type a predictably higher productivity potential and natural regeneration than the GRAY and MIXED spoil were its finer soil texture, higher CEC and P concentration, and a pH that was more suitable for native hardwood trees. Four species of tree seedlings were planted into the spoils. Growth and survival of the planted trees were evaluated for three years. As an indicator of natural succession potential, percentage ground cover of volunteer vegetation on the three spoil types was also evaluated. By the third year (2007) after planting, the BROWN spoil type had a significantly higher average tree volume index than the MIXED spoil and MIXED was significantly higher than GRAY. Ground cover from natural regeneration was found to be 66.4% on the BROWN spoil (61 different species), 5.8% on the MIXED spoil (35 different species), and less than 2.0% on the GRAY spoil (12 different species). Results showed that the loose-graded spoil in this experiment was characterized by low discharge volumes, small peak discharges, and long durations of discharge and had hydrologic characteristics of a forested watershed, even at this early stage of development. Generally, concentrations of Ca, Mg, and SO₄ ^2- decreased over time in GRAY and MIXED and increased in BROWN. The pH of the water discharge from all three spoil types has increased from about 7.5 to 8.5. Although the average electrical conductivity (EC) in water discharged from the BROWN spoil remained relatively level during the study period, the GRAY and MIXED appears to be on a downward trajectory from about 1500 μS cm^-1 to about 500 μS cm^-1. The latter value of EC has been reported as the apparent threshold at which the benthic invertebrate community returns to drastically disturbed headwater streams of eastern Kentucky and adjacent coal-producing Appalachian states.